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D.L. Smythe, J.C. Carter, A.E.E Rogers, J.E. Salah (MIT Haystack Observatory)
MIT Haystack Observatory is developing an electronically steerable, multi-beam array optimized for the 327 MHz deuterium line. The project requires the development of interference detection and rejection techniques which may benefit future arrays like SKA and LOFAR.
A monitoring system has been constructed to measure the level of RFI in a narrow band centered at 327.4 MHz. This system consists of an 8-channel digital receiver. Six of the channels are connected to Yagi antennas to determine the angle of arrival of the RFI, another channel is devoted to a low-noise active dipole pointed at the zenith, and the remaining channel is devoted to monitoring any RFI from the RFI monitor itself. The active dipole is a prototype of one of the elements of the array. Since the signal expected from the Deuterium Array is only about one milliKelvin, the RFI monitor is made sensitive to these levels by integrating the spectra over long periods of time. Most of the observed RFI is stray radiation from electronic equipment located at the Observatory and at private homes located within a mile of the array. Occasionally, signals of several thousand Kelvin are observed. While the monitor has been used to evaluate the level of RFI at the site in order to refine the design of the array, it will also be used during the operation of the array. The monitor will detect RFI at levels harmful to the array, but below those levels which can be removed automatically by the array. In this case, the monitor data can be used to delete these periods from the integration.
We are also developing a general-purpose monitor to measure RFI in the frequency range 30-1500 MHz with sufficient sensitivity to quantify the noise in protected receive-only bands.
This work is sponsored by the NSF.
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Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.